In an electrophotographic apparatus, e.g., a reproduction or printing machine, unfused toner images are formed on receiver members, and the toner images are then fused or fixed to receiver members in a fusing station employing heat and/or pressure. The receiver members are typically sheets of paper or transparency stock. The resulting output prints can be simplex (image on one side only) or duplex. A duplex print can be made by forming an unfused toner image on one side of a receiver member, fusing it, then forming an unfused toner image on the other side of the receiver member and fusing once again. Alternatively, an unfused image can be formed on each side of a receiver member and the toner images on both sides of the receiver member fused simultaneously in the fusing station so as to form a duplex print.
For full color high quality electrophotographic printing, it is known to employ a modular machine typically including, for example, at least four modules arranged in tandem fashion. In a 4-module machine, each module produces a respective single color toner separation image, e.g., a cyan, magenta, yellow, or black toner image. A receiver member is moved successively through the modules such that the respective single color toner images are sequentially transferred in registry to the receiver member. The receiver member can be electrostatically adhered to a transport belt, which transports the receiver member through the modules. Each module can include a primary imaging roller (imaging cylinder) and a compliant intermediate transfer member (blanket cylinder), as employed for example in the commercially available NexPress 2100 Digital Color Printer (NexPress Solutions LLC of Rochester, N.Y.).
Color prints made by electrophotographic reproduction apparatus, especially high gloss prints, can be subject to damage by a customer, e.g., by rubbing, abrasion, or scratching. This is particularly the case for high quality glossy photographic prints made from very small toner particles, for which the high quality can be compromised quite easily because the toner layers are comparatively thin and therefore more readily damaged. Moreover, a fused toner image on a receiver member can suffer from cracking damage when the print is bent. Hence there is a need to provide photographic quality prints which are more durable and resistant to the above-mentioned types of damage. In certain instances a print can be subject to fading, e.g., via exposure to ambient light which typically contains a UV component, and in such cases it is desirable to include in the printed image a UV-absorbing overcoat.
A common feature of electrophotographically produced color prints is a phenomenon known as “differential gloss”, whereby for example different areas within a pictorial image exhibit varying amounts of gloss. “Differential gloss” may encompass regions of high gloss and relatively low gloss, or even regions having little or no gloss. Customers tend to prefer uniformly glossed pictorial images. Equipment for making glossy toner images is known, and the degree of gloss or gloss level of a toner image can be quantitatively measured in a standard fashion using a specular glossmeter. Typically, a single reflectivity measurement is made which measures the amount of light from a standard source which is specularly reflected in a defined path. A suitable device for this purpose is a Glossgard II 20° glossmeter (available commercially from Pacific Scientific Inc., Silver Springs, Md.) which produces a reading, on a standardized scale, of a specularly reflected beam of light having angles of incidence and reflection of 20° to the normal. The glossmeter can measure gloss levels representing a dull matte to a very shiny finish. The usual range of measured gloss numbers on the meter is between 0 and 100, the instrument being normally calibrated or adjusted so that the upper limit corresponds to a surface that has substantially less than the complete specular reflection of a true mirror. Thus extremely smooth glossy surfaces can have gloss levels in excess of 100. Reflectivity readings are indicated as G20 gloss numbers (gloss levels). The larger the G20 number, the glossier the toner image.
For certain gloss measurements, for example of coatings, a glossmeter may be used in which the specularly reflected beam of light has angles of incidence and reflection of 60° to the normal, i.e., giving G60 numbers. The larger the G60 number, the glossier is the surface being measured.
It is known to make glossy electrophotographic prints via a number of methods utilizing various types of apparatus. Gloss can be imparted as a result of the fusing of toner particles in a fusing station, and in certain fusing equipment it is possible to control the amount of gloss. A belt fusing apparatus has been shown to be especially useful in this regard. In general, a belt fusing apparatus can include a heated roller, a steering roller of relatively smaller diameter, and a belt in tension around both heated roller and steering roller, with the belt passing through a pressure nip formed between the heated roller and a pressure roller. A hard heated roller and a compliant or resilient pressure roller can be used effectively for the belt fusing apparatus. Alternatively, a resilient heated roller can be used with a hard pressure roller. The heated roller is typically heated from within, e.g., by a lamp, although an externally heated roller can be used instead. A receiver member carrying a toner image for glossing is passed through the fusing nip with the toner facing the belt, and after leaving the nip the receiver member can be cooled while adhered to the belt via the adhesive properties of the toner. The receiver member can then be transported on the belt to the steering roller, whereupon the cooled receiver member can disengage from the belt, for example, as a result of the inherent stiffness of the receiver and a small radius of curvature of the steering roller.
The Namiki patent (U.S. Pat. No. 3,948,215) discloses a technique for providing gloss by fusing a toner image on a receiver by heat and pressure from a heatable surface in contact with the toner of the image. After fusing, the toner image is cooled while remaining in contact with the heatable surface. The receiver with the fused image is subsequently separated from the heatable surface without incurring the disadvantageous phenomenon of offset, i.e., in which a certain amount of toner material remains on the heatable surface after separation of the receiver therefrom.
In the Aslam, et al. patent (U.S. Pat. No. 5,256,507), a method of fusing a toner pattern to a receiver member is disclosed using a belt fusing apparatus, the toner pattern including at least one toner image for providing a low gloss and at least one toner image for providing a high gloss. The belt fusing apparatus includes a heated roller, a steering roller, and a fusing belt entrained around both rollers, with the fusing belt passing through a pressure nip formed between the heated roller and a pressure roller. The toner pattern on the receiver member is fused in the nip with the toner pattern facing the heated roller. In consequence of adhesive forces acting between the receiver member and the fused toner and between the toner and the belt, the receiver member is thereby transported from the nip through a cooling zone located between the heated roller and the steering roller such that the toner pattern cools while in contact with the belt. The receiver is separated from the belt as the belt passes around the steering roller, with the toner having been cooled in an airflow to a temperature at which offset does not occur. It is advantageous that the fusing of the toner image and the separation of the receiver member from the fusing apparatus are separate events.
The Aslam, et al. patent (U.S. Pat. No. 5,890,032) discloses a fusing accessory or glossing unit for use in conjunction with a reproduction apparatus (See also the Aslam, et al. patent (U.S. Pat. No. 6,026,274). In a conventional fusing mode within the reproduction apparatus, toner images on receiver members can be fused “in-line” using any suitable fusing mechanism. Alternatively, in a “parallel-line” fusing mode, toner images can be shunted through an attached glossing unit for fusing therein using a belt fuser arrangement for the controllable glossing of toner images. As another alternative, the fusing accessory can be employed as a stand-alone glossing unit for “off-line” glossing, i.e., with the accessory physically separated from the reproduction apparatus. For “off-line” glossing, fused prints such as pictorial prints produced by the conventional fusing are finished in the glosser accessory, e.g., loaded manually therein for glossing. The belt fuser arrangement of the glosser unit of U.S. Pat. No. 5,890,032 differs somewhat from that disclosed in the above-cited U.S. Pat. No. 5,256,507 in that in conjunction with use of a post-nip wrap of the belt on the heated roller, the degree or amount of glossing is controlled by controlling the amount of heat delivered per unit area per unit time in the fusing nip of the glosser.
An “in-line” belt fusing apparatus for controllable glossing, having a similarity to that of the belt fusing apparatus used in the glosser accessory of U.S. Pat. No. 5,890,032, is disclosed in the Aslam, et al. patent (U.S. Pat. No. 5,897,249).
The Aslam, et al. patents (U.S. Pat. Nos. 5,256,507, 5,890,032, 5,897,249) are hereby incorporated by reference.
The Kabashima patent (U.S. Pat. No. 6,512,914) discloses a glossing unit which is selectably attachable to a reproduction machine. The glossing unit includes a belt fusing apparatus for providing gloss to prints previously fused via conventional fusing in the reproduction machine. Prints are optionally sent to the glossing unit by diversion thereto from a path leading to an exit from the machine. After glossing, a print is moved to rejoin the path to the exit.
The Rohde, et al. patent (U.S. Pat. No. 6,594,465) and the Bartscher, et al. patent (U.S. Pat. No. 6,587,665) disclose apparatus and methods for delivering UV radiation to a toner image on a substrate for purpose of fusing the toner image to the substrate.
The Bartscher, et al. patent (U.S. Pat. No. 6,608,987) discloses method and apparatus for controlling a degree of luster of a toner layer or of a toner image fused to a substrate, especially cardboard or paper. Toner particles are used having a composition crosslinkable by UV radiation. The crosslinking or curing is carried out with the crosslinkable toner particles heated to an elevated temperature, notably above the glass transition temperature. The heating is carried out via IR radiation, the heating being done in a separate step prior to crosslinking the heated toner via UV radiation from a UV source. Thus the fixing of the toner to the substrate effectively combines contactless (radiant) fusing with UV curing such that the melting process and the curing process are independently controllable. A desired degree of luster can be obtained by controlling, e.g., via feedback, one or more of the variables of: pre-cure temperature, time for the crosslinking reaction, and UV power delivered per unit area. The toner layer on the substrate includes at least one UV-curable toner and can include toners of different colors.
Schulze-Hagenest, et al., in UV-cured Toners for Printing and Coating on Paper-like Substrates, 13th International Conference on Digital Printing Technologies (Imaging Science and Technology, 1997) pp. 168–172, disclose UV-curable toners for use to form durable prints on paper and cardboard substrates. Also described is apparatus for the UV curing (crosslinking) of such UV-curable toners at elevated temperatures, i.e., above the glass transition temperature (Tg) of the toner. A radiant fusing step, using IR radiation to heat the toner, is followed by a separate UV curing step in which the toner is in a molten or quasi-molten state. The IR pre-fusing provides a smooth film, while the subsequent UV curing reaction is very rapid. A curing temperature between approximately 70 C–80 C was sufficient, well above the Tg of the UV-crosslinkable toner. Schulze-Hagenest, et al. demonstrated the UV-curing of a thin IR-melted clear toner layer formed via magnetic brush development on a cardboard substrate (average toner thickness of 7.5 μm using 10.8 μm diam. toner particles). The process speed past a UV lamp was 10 cm/sec using a UV power density of about 1 Joule/cm2. The UV-crosslinkable toner was made using a polyester resin (830 parts w/w), a crosslinker (170 parts w/w), a photoinitiator (10 parts w/w) and a flowing agent (6 parts w/w), i.e., with a photoinitiator (sensitizer) doping of about 1.0% w/w. The process speed of 10 cm/sec was much lower than that typically used in a high speed electrophotographic color printer. However, it is stated that up to 3% w/w of sensitizer can be used.
UV-crosslinkable toner formulations are disclosed in the above-cited Bartscher, et al. patent (U.S. Pat. No. 6,608,987) and in the De Meutter, et al. patent (U.S. Pat. No. 5,905,012).
The May, et al. patent (U.S. Pat. No. 5,926,679) discloses that a clear (non-marking) toner layer can be laid down on a photoconductive member (e.g., imaging cylinder) prior to forming a marking particle toner image thereon, and that a clear toner layer can be laid down as a last layer on top of a marking particle toner image prior to transfer of the image to an intermediate transfer member (e.g., blanket cylinder). It is also disclosed that a clear toner layer can be laid down on a blanket cylinder prior to transferring a marking particle toner image from a photoconductive member thereon.
The use of transparent layers of toner particles in association with toner images for providing gloss for the fused images on receiver members is disclosed for example in the Ng patent (U.S. Pat. No. 5,234,783), the Buts, et al. patent (U.S. Pat. No. 5,506,671), the Aslam, et al. patent (U.S. Pat. No. 5,842,099), the Dalal patents (U.S. Pat. Nos. 6,167,224, 6,203,953, and 6,352,806), the Richards patent (U.S. Pat. No. 6,535,712) and the Maeyama, et al. patent (U.S. Pat. No. 6,678,493).
In the Aslam, et al. patent (U.S. Pat. No. 5,887,234), a reproduction machine including conventional fusing apparatus and a glosser fusing apparatus is disclosed in what may be called a “parallel-line” arrangement. The glosser fusing apparatus, which is a belt fusing apparatus, is selectable for making glossy output prints, i.e., is employed as alternative to the conventional fusing apparatus. The reproduction machine includes an intermediate transfer roller upon which a development station can form a layer of colorless toner when the glosser fusing apparatus is selected. An unfused multicolor toner image is built up in juxtaposition with the colorless toner layer, whereupon the colorless toner plus multicolor toner image are co-transferred to a receiver member and fused thereon in the glosser fusing apparatus. When glossing is not needed, the colorless toner layer is not deposited on the intermediate transfer roller, and an unfused multicolor toner image on the intermediate transfer roller is transferred to a receiver sheet which is sent to the conventional fusing apparatus.